To date the available therapies for the treatment of HIV infections have been leading to a remarkable improvement in symptoms and recovery from disease in infected people. Although the highly active anti retroviral therapy (HAART-therapy) which involves a combination of reverse transcriptase/protease inhibitor has dramatically improved the clinical treatment of individuals with AIDS or HIV infection there have still remained several serious problems including multi drug resistance, significant adverse effects and high costs. Particularly desired are anti HIV agents that block the HIV infection at an early stage of the infection, such as the viral entry.
It has recently been recognized that for efficient entry into target cells, human immunodeficiency viruses require the chemokine receptors CCR5 and CXCR4 as well as the primary receptor CD4 (N. Levy, Engl. J. Med., 335, 29, 1528-1530). Accordingly, an agent which could block the CXCR4 chemokine receptors should prevent infections in healthy individuals and slow or halt viral progression in infected patients (Science, 1997, 275, 1261-1264).
Among the different types of CXCR4 inhibitors (M. Schwarz, T. N. C. Wells, A.E.I. Proudfoot, Receptors and Channels, 2001, 7, 417-428), one emerging class is based on naturally occurring cationic peptide analogues derived from Polyphemusin II which have an antiparallel β-sheet structure, and a β-hairpin that is maintained by two disulfide bridges (H. Nakashima, M. Masuda, T. Murakami, Y. Koyanagi, A. Matsumoto, N. Fujii, N. Yamamoto, Antimicrobial Agents and Chemoth. 1992, 36, 1249-1255; H. Tamamura, M. Kuroda, M. Masuda, A. Otaka, S. Funakoshi, H. Nakashima, N. Yamamoto, M. Waki, A. Matsumotu, J. M. Lancelin, D. Kohda, S. Tate, F. Inagaki, N. Fujii, Biochim. Biophys. Acta 1993, 209, 1163; WO 95/10534 A1).
Synthesis of structural analogs and structural studies by nuclear magnetic resonance (NMR) spectroscopy have shown that the cationic peptides adopt well defined β-hairpins conformations, due to the constraining effect of the one ore two disulfide bridges (H. Tamamura, M. Sugioka, Y. Odagaki, A. Omagari, Y. Kahn, S. Oishi, H. Nakashima, N. Yamamoto, S. C. Peiper, N. Hamanaka, A. Otaka, N. Fujii, Bioorg. Med. Chem. Lett. 2001, 359-362). These results show that the β-hairpin structure plays an important role in CXCR4 antagonizing activity.
Additional structural studies have also indicated that the antagonizing activity can also be influenced by modulating amphiphilic structure and the pharmacophore (H. Tamamura, A. Omagari, K. Hiramatsu,. K. Gotoh, T. Kanamoto, Y. Xu, E. Kodama, M. Matsuoka, T. Hattori, N. Yamamoto, H. Nakashima, A. Otaka, N. Fujii, Bioorg. Med. Chem. Lett. 2001, 11, 1897-1902; H. Tamamura, A. Omagari, K. Hiramatsu, S. Oishi, H. Habashita, T. Kanamoto, K. Gotoh, N. Yamamoto, H. Nakashima, A. Otaka N. Fujii, Bioorg. Med.Chem. 2002, 10, 1417-1426; H. Tamamura, K. Hiramatsu, K. Miyamoto, A. Omagari, S. Oishi, H. Nakashima, N. Yamamoto, Y. Kuroda, T. Nakagawa, A. Otaki, N. Fujii, Bioorg. Med. Chem. Letters 2002, 12, 923-928).
A key issue in the design of CXCR4 antagonizing peptides is selectivity. The polyphemusin II derived analogs exert still a cytotoxicity despite improvements (K. Matsuzaki, M. Fukui, N. Fujii, K. Miyajima, Biochim. Biophys. Acta 1991, 259, 1070; A. Otaka, H. Tamamura, Y. Terakawa, M. Masuda, T. Koide, T. Murakami, H. Nakashima, K. Matsuzaki, K. Miyajima, T. Ibuka, M. Waki, A. Matsumoto, N. Yamamoto, N. Fujii Biol. Pharm. Bull. 1994, 17, 1669 and cited references above).
This cytotoxic activity essentially obviates its use in vivo, and represents a serious disadvantage in clinical applications. Before intravenous use can be considered, the general toxicity, protein-binding activity in blood serum, as well as protease stability become serious issues which must be adequately addressed.
Recently, it has been shown that the CXCR4-receptor is not only involved in the entry of HIV but also in the chemotactic activity of cancer cells, such as breast cancer metastasis or in metastasis of ovarian cancer (A. Muller, B. Homey, H. Soto, N. Ge, D. Catron, M. E. Buchanan, T. Mc Clanahan, E. Murphey, W. Yuan, S. N. Wagner, J. Luis Barrera, A. Mohar, E. Verastegui, A. Zlotnik, Nature 2001, 50, 410, J. M. Hall, K. S. Korach, Molecular Endocrinology, 2003, 1-47), Non-Hodgin's Lymphoma (F. Bertolini, C. DellAgnola, P. Manusco, C. Rabascio, A. Burlini, S. Monestiroli, A. Gobbi, G. Pruneri, G. Martinelli, Cancer Research 2002, 62, 3106-3112), or lung cancer (T. Kijima, G. Maulik, P. C. Ma, E. V. Tibaldi, R: E. Turner, B. Rollins, M. Sattler, B. E. Johnson, R. Salgia, Cancer Research 2002, 62, 6304-6311), melanoma, prostate cancer, kidney cancer, neuroblastomia, pancreatic cancer, multiple myeloma, chronic lymphocytic leukemia (H. Tamamura et al. Febs Letters 2003, 550 79-83, cited ref.) Blocking the chemotactic activity with a CXCR4 inhibitor should stop the migration of cancer cells.
The CXCR4 receptor has also been implicated in the growth and proliferation of tumors. It was shown that activation of the CXCR4 receptor was critical for the growth of both malignant neuronal and glial tumors, and small cell lung tumors. Moreover, systemic administration of the CXCR4 antagonist AMD3100 inhibits growth of intracranial glioblastoma and medulloblastoma xenografts by increasing apoptosis and decreasing the proliferation of tumor cells (Rubin J B, Kung A L, Klein R S, Chan J A, Sun Y, Schmidt K, Kieran M W, Luster A D, Segal R A. Proc Natl Acad Sci USA. 2003 100(23):13513-13518, Barbero S, Bonavia R, Bajetto A, Porcile C, Pirani P, Ravetti J L, Zona CL, Spaziante R, Florio T, Schettini G. Stromal Cancer Res. 2003, 63(8):1969-1974, Kijima T, Maulik G, Ma P C, Tibaldi E V, Turner R E, Rollins B, Sattler M, Johnson B E, Salgia R. Cancer Res. 2002;62(21):6304-631 1, Cancer Res. 2002;62(11):3106-3112.
The chemokine stromal cell-derived factor-1 (CXCL12/SDF-1) and its receptor CXCR4 are involved in trafficking of B cells and hematopoietic progenitors. It has been shown that the CXCR4 receptor plays an important role in the release of stem cells from the bone marrow to the peripheral blood. The receptor is for instance expressed on CD34+ cells, and has been implicated in the process of CD34+ cell migration and homing. This activity of the CXCR4 receptor could be very important for efficient apheresis collections of peripheral blood stem cell. Autologous peripheral blood cells provide a rapid and sustained hematopoietic recovery following autotransplantation after the administration of high-dose chemotherapy or radiotherapy in patients with haematological malignancies and solid tumors. (W C. Liles et al, Blood 2003, 102, 2728-2730).
There is increasing evidence that suggests that chemokines in general and the interaction between the chemoattractant CXCL12/stromal cell-derived factor-I alpha and its receptor CXCR4 in particular play a pivotal role in angiogenesis. Chemokines induce angiogenesis directly by binding their cognate receptors on endothelial cells or indirectly by promoting inflammatory cell infiltrates, which deliver other angiogenic stimuli. A number of proinflammatory chemokines including interleukin 8 (IL-8), growth-regulated oncogene, stromal cell-derived factor 1 (SDF-1), monocyte chemotactic protein 1 (MCP-1), eotaxin 1, and I-309 have been shown to act as direct inducers of angiogenesis. (Chen X, Beutler J A, McCloud T G, Loehfelm A, Yang L, Dong H F, Chertov O Y, Salcedo R, Oppenheim J J, Howard O M. Clin Cancer Res. 2003 9(8):3115-3123, Salcedo R, Oppenheim J J. Microcirculation 2003 (3-4):359-370)
It is well established that chemokines are involved in a number of inflammatory pathologies and some of them show a pivotal role in the modulation of osteoclast development. Immunostaining for SDF-1 (CXCL12) on synovial and bone tissue biopsies from both rheumatoid arthritis (RA) and osteoarthritis (OA) samples have revealed strong increases in the expression levels under inflammatory conditions. (Grassi F, Cristino S, Toneguzzi S, Piacentini A, Facchini A, Lisignoli G. J Cell Physiol. 2004; 199(2):244-251. It seems likely that the CXCR4 receptor plays an important role in inflammatory diseases e.g. such as rheumatoid arthritis, asthma, or multiple sclerose (K. R. Shadidi et al, Scandinavian Journal of Immunology, 2003, 57, 192-198, J. A. Gonzalo J Immunol. 2000, 165, 499-508, S. Hatse et al, FEBS Letters 2002 527, 255-262 and cited references).
The mediation of recruitment of immune cells to sites of inflammation should be stopped by a CXCR4 inhibitor.
In the compounds described below, a new strategy is introduced to stabilize beta-hairpin conformations in cyclic backbone-turn peptidomimetics exhibiting high CXCR4 antagonizing activity, being useful for efficient apheresis collections of peripheral blood stem cells, and having anticancer activity and anti inflammatory activity.
This involves transplanting the cationic and hydrophobic hairpin sequence onto a template, whose function is to restrain the peptide loop backbone into a hairpin geometry. The rigidity of the hairpin may be further influenced by introducing a disulfide bridge. Template-bound hairpin mimetic peptides have been described in the literature (D, Obrecht, M. Altorfer, J. A. Robinson, Adv. Med. Chem. 1999, 4, 1-68; J. A. Robinson, Syn. Lett. 2000, 4, 429-441), but such molecules have not previously been evaluated for development of CXCR4 antagonizing peptides. However, the ability to generate β-hairpin peptidomimetics using combinatorial and parallel synthesis methods has now been established (L. Jiang, K. Moehle, B. Dhanapal, D. Obrecht, J. A. Robinson, Helv. Chim. Acta. 2000, 83, 3097-3112).
These methods allow the synthesis and screening of large hairpin mimetic libraries, which in turn considerably facilitates structure-activity studies, and hence the discovery of new molecules with highly potent CXCR4 antagonizing activity or anti cancer activity or anti inflammatory activity and low hemolytic activity to human red blood cells.
β-Hairpin peptidomimetics obtained by the approach described here are useful as Anti-HIV agents, anticancer agents, as inhibitors of tumor growth or as apoptosis inducing agents, anti-metastasis agents, and anti inflammatory agents or as agents that can be used in apheresis collections of peripheral blood stem cells. The β-hairpin peptidomimetics can be used for preventing HIV infections in healthy individuals or for slowing and halting viral progression in infected patients; or where cancer is mediated or resulting from CXCR4 receptor activity; or where immunological diseases are mediated or resulting from CXCR4 receptor activity; or for treating immunosuppression; or during apheresis collections of peripheral blood stem cells.